Olefin polymerization process in the presence of an anti-fouling agent

ABSTRACT

An olefin polymerisation process carried out in the presence of an anti-fouling agent and a chromium-type catalyst or Ziegler Natta catalyst; characterised in that the anti-fouling agent comprises an anti-fouling polymer having an average molecular weight (Mw) of greater than 1000 daltons and containing: (1) one or more blocks —(CH 2 —CH 2 —O) k — where each k is in the range from 1 to 50; and (2) one or more blocks —(CH 2 —CH(R)—(O) n   −  where R comprises an alkyl group having from 1 to 6 carbon atoms and each n is in the range from 1 to 50, and terminated by a R′ and a R″ end groups, wherein R′ is OH or an alkoxy having from 1 to 6 carbon atoms and R″ is H or an alkyl having from 1 to 6 carbon atoms.

The present invention concerns a new olefin polymerisation process forpreventing fouling in the polymerisation reactor. The inventionparticularly concerns olefin polymerisation processes usingchromium-oxide-type (so-called Phillips type) or a Ziegler Natta-typecatalyst.

Olefin polymerisation processes are well known. Among the processes,slurry polymerisation in suspension in a solvent or in the liquidmonomer is extensively practiced. Such processes are performed in astirred tank reactor, or in closed loop reactors. One or more reactorscan be used. In such processes, solid polymer particles are grown onsmall catalyst particles. Released heat of polymerisation is eliminatedthrough cooling through the reactor's walls and/or a heat exchanger.

However, it has been found on an industrial scale that while the polymerparticles are insoluble or substantially insoluble in the diluent, thepolymer product has some tendency to deposit on the walls of thepolymerisation reactor. This so-called “fouling” leads to a decrease inthe efficiency of heat exchange between the reactor bulk and the coolantaround the reactor. This leads in some cases to loss of reactor controldue to overheating, or to reactor or downstream polymer processingequipment failure due to formation of agglomerates (ropes, chunks).

This “fouling” is caused in part by fines and also by the build up ofelectrostatic charge on the walls on the reactor. Attempts to avoidfouling during slurry polymerisation have been made by adding anantifouling agent in the polymerisation medium. Typically, theantifouling agent acts for example to make the medium more conductive,thus preventing to some extent the formation of electrostatic charge,which is one cause of the build-up of polymer on the wall of thereactor.

U.S. Pat. No. 3,995,097 discloses a process whereby an olefin ispolymerised in a hydrocarbon diluent using a catalyst comprisingchromium oxide associated with at least one of silica, alumina,zirconia, or thoria. Fouling of the reactor is said to be reduced byadding a composition, which comprises a mixture of aluminium or chromiumsalts of an alkyl salicylic acid and an alkaline metal alkyl sulphursuccinate.

EP 0,005,215 is concerned with a process for polymerising olefins in ahydrocarbon diluent again using a catalyst comprising calcined chromiumcompound associated with at least one of silica, alumina, zirconia orthoria or using a catalyst system such as those disclosed in U.S. Pat.Nos. 2,908,671, 3,919,185 and 3,888,835. The process uses ananti-fouling agent comprising a compound containing a sulphonic acidresidue. The anti-fouling agent is a composition comprising (a) apolysulphone copolymer (b) a polymeric polyamine, and (c) an oil solublesulphonic acid. In the Example, the additive product known as Stadis 450is used as the anti fouling agent.

U.S. Pat. No. 6,022,935 (equivalent to EP 0,803,514) discloses a processfor the preparation of polymers of C₂-C₁₂ alk-1-ene using a catalystsystem containing a metallocene complex. An antistatic agent is used inthe process. It is said that in general, all antistatic agents which aresuitable for polymerisations may be used. Examples given are saltmixtures comprising calcium salt s of medialanic acid and chromium saltsof N-stearylanthranilic acid, C₁₂-C₂₂ fatty acid soaps of sulfonicesters of the general formula (RR′)—CHOSO₃Me, esters of polyethyleneglycols with fatty acids, and polyoxyethylene alkyl ethers.

EP 0,820,474 is concerned with preventing sheeting problems in gas phasereactors in polymerisation processes, which comprise at least one loopreactor followed by at least one gas phase reactor. These problems areaddressed using a fouling preventive agent that is a mixture of Cr saltof C₁₄-C₁₈ alkyl-salicylic acid, a Ca dialkyl sulphosuccinate and acopolymer of alkylmethacrylate with 2-methyl-5-vinylpyridine in solutionin xylene. Chromium-type catalysts, Ziegler-type catalysts andmetallocene catalysts are mentioned.

JP 2000-327,707 discloses a slurry olefin polymerisation method. Themethod addresses the problems of fouling and sheeting of the reactorwall, which is observed particularly with supported metallocenecatalysts. The method is said to be carried out in the presence of onecompound chosen from polyalkylene oxide alkyl ether, alkyldiethanolamine, polyoxyalkylene alkyl amine, and polyalkylene oxideblock.

EP 1 316 566 discloses propylene polymerisation in a bulk loop reactor.The disclosure is concerned specifically with the transition from onecatalyst type to another in a bulk loop reactor and with the problemsassociated therewith. The process involves injecting a metallocenecatalyst and a Ziegler-Natta catalyst system into the bulk loop reactor.There is no disclosure in EP 1316566 of the catalyst being achromium-oxide type catalyst. It is mentioned on page 3 paragraph [0009]that in one embodiment, a volume of antifouling agent may be introducedinto a catalyst mixing system. Three possible antifouling agents arementioned. The discussion on pages 10 and 11 clearly teach that anantifouling agent is used for the metallocene catalyst systems and notfor conventional Ziegler-Natta catalyst systems. Further, themetallocene catalyst and Ziegler-Natta catalyst are injected into theloop reactor sequentially in EP 1 316 566 and not simultaneously so thatthey are not both present in the reactor at the same time and so thatany antifouling agent present in the metallocene catalyst system willnot contact the Ziegler-Natta catalyst system.

In view of the above, it will be seen that many so called anti-foulingagents for use in various olefin polymerisation processes are known.However, there have been some problems associated with prior knownagents, particularly in relation to polymerisation processes usingchromium-type catalysts and sometimes Ziegler-Natta type catalysts.These problems include an increase of catalyst consumption due to lossof activity in the presence of the anti-fouling agent. This can beobserved even at the low levels typically used in the polymerisationprocess. Catalyst activity loss is linked to the poisoning of activesites, for example by the polar moieties of the anti-fouling agent(alcohol and sulphonate . . . ).

Other problems with prior known agents relate to problems of toxicity.This is a particular concern with Cr-based anti-fouling agent or withagents such as commercial Stadis 450 as described in EP 0,005,215,because of the solvent type (toluene) and/or because of the activeingredient.

Finally, practical problems are encountered with many previously knownanti-fouling agents. These practical problems arise because someantifouling agents are usable only with a given catalyst type. Thismakes transitions between catalyst systems during processing moredifficult.

Thus, there remains a need to provide new anti-fouling agents for use inolefin polymerisation processes using chromium-type catalysts, lateTransition Metal-type catalysts, or Ziegler-Natta type catalysts withoutthe drawbacks of current products.

This problem has been solved at least partially by the provision of anolefin polymerisation process carried out in the presence of ananti-fouling agent and a chromium-type catalyst, a late Transition Metaltype catalyst, or Ziegler Natta catalyst; characterised in that theanti-fouling agent comprises an anti-fouling polymer having an averagemolecular weight (Mw) of greater than 1000 daltons and containing:

-   -   (1) one or more —(CH₂—CH₂—O)_(k)— where each k is in the range        from 1 to 50; and    -   (2) one or more —(CH₂—CH(R)—O)_(n)— where R comprises an alkyl        group having from 1 to 6 carbon atoms and each n is in the range        from 1 to 50,        and terminated by a R′ and a R″ end groups, wherein R′ is OH or        an alkoxy having from 1 to 6 carbon atoms an d R″ is H or an        alkyl having from 1 to 6 carbon atoms.

In the present process, (CH₂CH(R)O)_(n) blocks generally may beconsidered to be lipophilic whereas (CH₂CH₂O)k blocks may be consideredto be hydrophilic. Preferably, one end of the polymer is hydrophilic andthe other end or the middle of the polymer is lipophilic.

Such an anti-fouling agent is known per se, particularly outside thefield of olefin polymerisation. In this regard, such an agent is knownas a washing detergent.

However, it has been surprisingly found by the present inventors thatsuch an agent may be used advantageously in an olefin polymerisationmethod which uses a chromium-type catalyst, a late Transition Metal-typecatalyst, or Ziegler-Natta type catalyst. In particular it has been unexpectedly found that improved activity of the catalyst occurs when thisanti-fouling agent is used in a process, which uses a chromium-typecatalyst, as compared with using other known anti fouling agents such asStadis 450. In fact, up to twice the activity has been observed. This isespecially unexpected because catalyst poisoning in presence of ananti-fouling agent is a particular problem with chromium-type catalystsbecause no scavenger such as a metal alkyl is used.

Furthermore, it has been found that no loss of activity occurs when thisanti-fouling agent is used in a process, which uses a late TransitionMetal-type catalyst or a Ziegler-Natta type catalyst. This isparticularly advantageous since, for logistical reasons, it ispreferable to be able to use a single anti-fouling agent in olefinpolymerisation processes regardless of the type of catalyst (i.e.chromium-type, late Transition Metal-type, Ziegler-Natta type ormetallocene. This is however not possible with most previously knownanti-fouling agents, without loss of activity with one of the catalysttypes.

Also, importantly, the rheology and mechanical properties of the resinproduct are not substantially modified when the present anti-foulingagent is used.

The present anti-fouling agent has the further advantage in that it issafer to humans than Cr-compounds or agents using an aromatic diluent,for example. This is in part because the present anti-fouling agent doesnot necessarily require a solvent, thereby avoiding the presence of forexample toluene.

Preferably, the anti-fouling polymer is a block polymer, more preferablya triblock polymer.

Preferably, the antifouling polymer is a block polymer of generalformula:R′—(CH₂—CH₂—O)_(k)—(CH₂—CH(R)—O)_(n)—(CH₂—CH₂—O)_(m)—R″  (I)orR′—(CH₂—CH(R)—O)_(a)—(CH₂—CH₂—O)_(b)—(CH₂—CH(R)—O)_(c)—R″  (II)where R comprises an alkyl group; R′ and R″ are end groups; k is from 1to 50; n is from 1 to 50; m is greater than or equal to 1; a is from 1to 50; b is from 1 to 50; and c is from 0 to 50; k and m and a and c maybe the same or different.

Preferably R is a C1 to C3 alkyl group. More preferably, R is a methylgroup.

Preferably, in one embodiment, k is greater than 1 and m is greaterthan 1. Also preferably, in another embodiment a is 0 or c is 0.

Preferred R′ and R″ groups include H; OH; alkyl, and alkoxy groups.Preferred alkyl groups are C1 to C3 alkyl groups. Preferred alkoxygroups are C1 to C3 alkoxy groups. In this regard, as mentioned above,the ends of the polymer should be hydrophilic. Therefore, in formulae(I) and (II) above, it is preferred that R′ is OH or an alkoxy group,preferably OH or a C1 to C3 alkoxy group. Further, it is preferred thatR″ is H or an alkyl group, preferably H or a C1 to C3 alkyl group.

A particularly preferred polymer has general formula (III):R′—(CH₂—CH₂—O)_(k)—(CH₂—CH(CH₃)—O)_(n)—(CH₂—CH₂—O)_(m)—R″  (III)where R′, R″, k, n, and m independently are as defined anywhere above.

A further preferred polymer has general formula (IV):OH—(CH₂—CH₂—O)_(k)—(CH₂—CH(R)—O)_(n)—(CH₂—CH₂—O)_(m)—H  (IV)where R, k, n, and m independently are as defined anywhere above.

It will be appreciated that, by virtue of the preferred molecularweights for the present anti-fouling polymer and the preferred ethyleneoxide contents in the pre sent anti-fouling polymer given above,preferred values for a, b, c, k, n, and m can be derived.

It will be understood in the present process that, where necessary, anactivating agent will be needed to activate the catalyst (e.g;Ziegler-Natta catalyst) or to modify the product polymer properties.Suitable activating agents, where needed, are well known in this art.Suitable activating agents include organometallic or hydride compoundsof Group I to III, for example those of general formula AlR₃ such asEt₃Al, Et₂AlCl, and (i-Bu)₃Al. One preferred activating agent istriisobutylaluminium.

When the polymerisation process is a slurry polymerisation process, itis carried out in suspension in a liquid diluent. The diluent can be theliquid monomer or comonomer per se (e.g. propylene, hexene), or an inertliquid such as an alkane. Preferred alkane diluents include isobutane,propane, butane, pentane, hexane, isohexane, cyclohexane, and mixturesthereof.

The anti-fouling agent may be added at any suitable st age in theprocess. The addition can be carried out continuously or batch wise. Theanti-fouling agent may be added to the polymerisation medium separatelyor may be mixed with the monomer or with the comonomer and then added tothe polymerisation medium. Advantageously, the anti-fouling agent may beadded via the monomer header in order to introduce the agent evenly inthe reactor.

The anti-fouling agent desirably is liquid at room temperature and, assuch, the anti-fouling polymer is liquid at room temperature. There aretwo principle factors which determine whether the anti-fouling polymeris liquid at room temperature. These are: the molecular weight of theanti-fouling polymer and the wt % ethylene oxide in the anti-foulingpolymer.

Preferably, the wt % ethylene oxide in the anti-fouling polymer is inthe range of from 5 to 40 wt %, more preferably from 8 to 30 wt %, evenmore preferably from 10 to 20 wt %, most preferably about 10 wt %.

Further, the anti-fouling polymer preferably has a molecular weight(MW), not higher than 5000. In order to avoid any poisoning effect onthe catalyst and to minimise elution of residues from the formed polymerproduct, the molecular weight is greater than 1000 Daltons, preferablygreater than 2000 Daltons, more preferably in the range from 2000-4500Daltons.

It will be understood from the above that in order to ensure that theanti-fouling agent is liquid at room temperature, one must balance themolecular weight of the anti-fouling polymer and the wt % ethylene oxidein the anti-fouling polymer. It is to be noted that the activity of theanti-fouling polymer decreases as the molecular weight increases.Therefore, in practice, it may be desirable to increase the wt %ethylene oxide in the anti-fouling polymer in order to ensure that theanti-fouling agent is liquid at room temperature, rather than increasethe molecular weight of the anti-fouling polymer.

It will be appreciated from the above that the molecular weight of theanti-fouling polymer should be selected in combination with the wt %ethylene oxide content in the anti-fouling polymer. For guidance value,the present inventors have found that an anti-fouling polymer having anethylene oxide content of 10 wt % and a molecular weight in the range offrom 4000 to 4500 is particularly useful in the present process.

Generally, the anti-fouling polymer is used at the lowest possibleconcentration effective to prevent or substantially reduce fouling. Thiscan be determined by routine experimentation. Preferably it is used at aconcentration of from 0.5 to 20 ppmw in the polymerisation medium, morepreferably from 2 to 10 ppmw.

Preferably the present process may be used to make homopolymers ofethylene or copolymers or higher order polymers of ethylene and one ormore comonomers. The copolymer or higher order polymer may be in arandom, alternating, or block configuration. Preferred comonomers arealpha olefins including, for example, propylene, 1-butene, 1-hexene,4-methyl 1-pentene, 1-octene. The process can further be used to makehomopolymers or copolymers of other alpha olefins, for examplepropylene, butene and the like. It has been found that the presentprocess is particularly effective when making high density polyethylene,although the process is not so limited.

Where the copolymer or higher order polymer is in a block configuration,one way of making the polymer is to make the homopolymer “blocks” and,subsequently, to introduce these pre-made “blocks” into thepolymerisation medium with a comonomer. Alternatively, the “block”polymer can be made in a polymerisation medium containing the propylenemonomer with a small quantity of the comonomer.

A preferred reaction temperature range may be said to be from 40° C. to130° C., preferably from 50 to 120° C., more preferably from 70 to 110°C. for ethylene polymers.

A preferred applied pressure range may be said to be from 5 to 200 bars,more preferably from 30 to 70 barg, depending on the reactorconfiguration and on the diluent.

Generally, chromium-type catalysts usable in the present processcomprise a chromium-oxide type catalyst, preferably chromium oxideassociated with at least one of silica, alumina, titania,aluminophosphate or thoria. Such catalysts are well known in the art.Preferred chromium-oxide-type catalysts include Cr on silica, Cr onsilica doped with titania, alumina, aluminophosphate, fluorine ormixtures thereof, and Cr on aluminophosphate.

Late transition metal catalysts usable in the present process includenickel complexes and iron complexes such as disclosed for example inIttel et al. (S. T. Ittel, L. K. Johnson and M. Brookhart, in Chem.Rev., 2000, 1169.) and in Gibson and Spitzmesser (V. C. Gibson and S. K.Spitzmesser, in Chem. Rev., 2003, 283.). Catalysts of this type will bewell known to a person skilled in this art.

Generally, Ziegler-Natta type catalysts usable in the present processcomprise a transition metal compound of Group IV-VIII (mainly Ti, Zr orV) supported on a carrier. Such catalysts are well known in the art.Examples of Ziegler-Natta catalysts are TiCl₄, TiCl₃, VCl₄, VOCl₃.Titanium chloride supported on a MgCl₂ support or a MgCl₂/silica supportare preferred.

One bulk reactor type which may be applied in slurry polymerisationprocesses is a turbulent flow reactor such as a continuous pipe reactorin the form of a loop. A continuous pipe reactor in the form of a loopis operated in liquid full mode, using liquid monomer or a diluent asthe liquid medium. Such a so-called loop reactor is well known and isdescribed in the Encyclopedia of Chemical Technology, 3^(rd) edition,vol. 16 page 390. This can produce LLDPE and HDPE resins in the sametype of equipment.

A loop reactor may be connected to one or more further reactors, such asanother loop reactor. A loop reactor that is connected to another loopreactor may be referred to as a “double loop” reactor.

Other types of bulk reactors such as stirred tank reactors may be usedinstead of a loop reactor, again using the bulk monomer or a diluent asthe liquid medium. A stirred tank reactor also may be used incombination with a loop reactor, where a first reactor that is a loopreactor is connected to a second reactor that is a stirred tank reactor.

In some cases it may be advantageous for a gas phase reactor also to beincorporated. The gas phase reactor may be a second reactor that isconnected to a first reactor such as a loop reactor or a stirred tankreactor. Alternatively, a gas phase reactor may be connected as a thirdreactor in the apparatus. In the gas phase reactor (if present), theelastomeric part of a copolymer or higher order polymer product may beproduced. The elastomeric part of the polymer product gives impactproperties to the product. The elastomeric part of the polymer producttypically is comonomer rich.

The bulk reactor(s) may be connected to a gas phase reactor, for examplewhere it is desirable to prepare a “block” polymer.

The present invention now will be described in further detail withreference to the attached drawings in which:

FIG. 1 shows the results of rheological dynamic analysis (RDA), Gcexpressed in Pa·s as a function of Wc expressed in rad/s performed onresins A and D.

FIG. 2 shows the results of RDA Gc expressed in Pa·s as a function of Wcexpressed in rad/s performed on resins B and C

FIG. 3 shows a loop reactor usable in a process according to the presentinvention.

The following embodiment describes a loop reactor system:

-   -   A monomer (for example ethylene) polymerises in a liquid diluent        (for example isobutane), hydrogen, catalyst, activating agent,        anti-fouling agent, and optionally in the presence of a        comonomer (for example hexene). A reactor essentially consists        of four or more vertical jacketed pipe sections (1 a, 1 b, 1 c,        1 d, 1 e, 1 f) connected by trough elbows (3 a, 3 b, 3 c, 3 d, 3        e, 3 f), see FIG. 3 which shows a reactor with six vertical        jacketed pipe sections. There are three lower trough elbows in        the reactor in FIG. 3 (3 b, 3 d, 3 f) and three upper trough        elbows (3 a, 3 c, 3 e). The slurry is maintained in circulation        in the reactor by an axial pump (2). The polymerisation heat may        be extracted by water cooling jackets around the vertical pipe        sections (legs). The reactants, diluent and antifouling agent        conveniently are introduced into one of the lower trough elbows        of the reactor. Typically, the reactants, diluent and        antifouling agent are introduced close to the circulating pump,        for example in position “4”, as shown in FIG. 3.    -   The product (for example polyethylene) may be taken out of one        or more of the lower trough elbows of the reactor, with some        diluent. Typically, the product is removed from a different        trough elbow to the trough elbow into which the reactants,        diluent and antifouling agent are introduced. For example, in        FIG. 3, when the reactants, diluent and antifouling agent are        introduced at position “4”, the product could be removed from        trough elbow 3 b or 3 d.

Slurry removal can be performed using a wash column or centrifugeapparatus.

Alternatively, slurry removal can be performed through settling legs anddiscontinuous discharge valves. In this discontinuous discharge system,a small fraction of the total circulating flow is withdrawn.

Alternatively, a continuous discharge system can be used.

If run in series, the product of the first loop reactor collectedthrough the slurry removal system is reinjected in the second reactorwith additional diluent and monomer. If required, additional antifoulingagent can also be added to the second reactor. A concentration of theslurry between the reactors can sometimes be performed, e.g. through theuse of hydro-cyclone systems.

If the slurry does not need to be transferred to another reactor, it ismoved to a polymer degassing section in which the solid content isincreased.

-   -   While being depressurised, the slurry is degassed, for example        during transfer through heated flash lines to a flash tank. In        the flash tank, the product and diluent are separated. The        degassing is completed in a purge column. The powder product is        then further additivated and processed into pellets or        additivated powder.

EXPERIMENTS I Comparison of Present Antifouling Agent with Stadis 450

Methods

Four resins (A-D) were produced using essentially two differentanti-fouling agents, as follows:

Resin A: a bimodal resin produced using 2.2 ppm Stadis 450 (RTM) in IC4;

Resin B: a film resin produced using 2.4 ppm Stadis 450 (RTM) in IC4;

Resin C: a film resin produced using 1.1 ppm anti-fouling agent I (AFAI)in isobutene (IC4);

Resin D: a bimodal resin produced using 1.0 ppm anti-fouling agent I(AFAI) in IC4.

Anti-fouling agent I (AFAI) was in accordance with the present inventionand had a formula:

Anti-fouling Agent I had an OH value of 25.5 mg kOH/g, an approximateM_(w) of 4400, and a 10% w/w ethylene oxide content.

The concentrations of anti-fouling agent I in IC4 and Stadis 450 (RTM)in IC4 were calculated so as to introduce the same amount of activecompound into the reactor in each case. In this regard, Stadis 450 (RTM)contains about 50% toluene whereas anti-fouling agent I contained nosolvent.

The anti-fouling agents (AF) were tested in a polymerisation reactionusing a Cr on silica-titania catalyst (2.5% titania, 1% Cr, SA of about500 m²/g and pore volume of 2.5 ml/g.). Activation was performed in afluidised bed, under air flow for 6 hours, at a given temperature.Complete details of the polymerisation process are provided in Tables 1and 2 for each of resins A to D.

The reactor parameters and analysis are summarised in Table 1 below.

TABLE 1 Resin A Resin D Run Stadis AFAI reactor conditions CATALYSTdumps/h 60.5 26.5 TEMP. ° C. 96.5 97 ALKYL ppm 1.7 1.4 C2− kg/h 9.0 9.0C6− Kg/h 0.170 0.108 IC4 Kg/h 24 24 AF ppm 2.2 1.0 ANALYSIS OF EXITINGC2− wt % 4.81 4.39 GAS C6− wt % 0.27 0.24 C6−/C2− 0.057 0.054 LOOPANALYTICAL MI2 g/10′ 0.077 0.060 RESULTS HLMI g/10′ 8.9 6.6 SR2 =HLMI/MI2 116 110 DENSITY g/cc 0.9514 0.9501 Bulk Density (BD) (g/cc)0.433 0.403 ANALYSIS OF Productivity measured g/g 1005 2217 HOMOGENISEDFLUFF by X-ray fluorescence (Prod XRF) Activity, calculated from g/g/h/%C2 183 443 productivity (Activity XRF) Waxes % 5.9 4.8 MI2 g/10′ 0.0880.0589 HLMI g/10′ 10.2 6.9 SR2 = HLMI/MI2 116 117 Density g/cc 0.95360.9508

Resins A and D were produced at the same reactor temperature, equivalentalkyl concentration and the same C₂ off-gas. In these experiments, themelt indices MI2 and HLMI were measured following the method of standardtest ASTM D 1238 at a temperature of 190° C. and under a load ofrespectively 2.16 kg and 21.6 kg. The density was measured following themethod of standard test ASTM D 1505 at a temperature of 23° C. and thebulk density Bd was measured following the method of standard test ASTMD 1895.

The antifouling agent I as compared to Stadis 450 (RTM) has a lowerpoisoning effect, gives higher catalyst productivity and generates lowermelt index potential.

After fluff homogenising, a higher HLMI and density was measured forresin A.

Waxes content was equivalent for both resins A and D.

TABLE 2 Resin B Resin C Run Stadis AFAI reactor conditions CATALYSTdumps/h 35.3 36.9 TEMP. ° C. 90.5 90.5 ALKYL ppm 1.8 1.7 C2− kg/h 9.09.0 C6− Kg/h 0.983 1.044 IC4 Kg/h 24 24 AF ppm 2.4 1.1 ANALYSIS OFEXITING C2− wt % 5.5 5.41 GAS C6− wt % 1.98 2.09 C6−/C2− 0.368 0.391LOOP ANALYTICAL MI2 g/10′ 0.158 0.155 RESULTS HLMI g/10′ 16.5 15.4 SR2108 101 DENSITY g/cc 0.9342 0.9348 Bulk Density (BD) g/cc 0.433 0.408ANALYSIS OF Prod XRF g/g 1463 1622 HOMOGENISED FLUFF Activity XRFg/g/h/% C2 233 263 Waxes % 24.4 27.5 MI2 g/10′ 0.1488 0.1535 HLMI g/10′14.7 15.5 SR2 99 101 Density g/cc 0.9373 0.9376

Resins B and C were produced at the equivalent reactor conditions asshown in Table 2. No significant difference was observed between theanti-fouling agents in resins B and C in terms of properties andproductivity, although approximately 10% higher productivity wasachieved using anti-fouling agent I in resin C.

Resin Properties

Gel Permeation Chromatography (GPC) and Rheological Dynamic Analysis(RDA) were performed on all the resins.

Due to low productivity, the molecular weight distribution (MWD) ofresin A is broad (see GPC results in Table 3), the weight averagemolecular weight (Mw) being equivalent. Taking into account the meltdifference (8.8 g/10′ with the anti-fouling agent in resin D and 14.3with the anti-fouling agent in resin A) and the equivalent SR2, morelong chain branching is generated with the anti-fouling agent in resin Dand this is related to the higher catalyst productivity. All propertieswere measured on pellets.

TABLE 3 Resin A Resin D Run Units Stadis AFAI Mn 11725 14363 Mw 216965213259 Mz 2481877 1743835 D = Mw/Mn 18.5 14.8 D′ = Mz/Mw 11.4 8.2 HLMIg/10′ 14.3 8.8 Wc (COP-RDA) rad/s 0.71 0.373 Gc (COP-RDA) Pa · s 1369012590

Mn, Mw and Mz represent respectively the number average molecularweight, the weight average molecular weight and the z average molecularweight. RDA results confirm that the Melt Index of resin A is too highand that resin D contains more long chain branching and/or has anarrower MWD (see FIG. 1) GPC and RDA curves show that film resins B andC are equivalent (see Table 4 and FIG. 2). MWD are broad for both resinsindicating low productivity.

TABLE 4 Resin B Resin C Run Units Stadis AFAI Mn 13059 13471 Mw 201926282173 Mz 2119213 4998934 D = Mw/Mn 15.5 20.9 D′ = Mz/Mw 10.5 17.7 MI2g/10′ 0.12 0.12 HLMI g/10′ 15.6 15.4 SR2 130 128 density 0.9372 0.9370Wc (COP-RDA) rad/s 2.1 2.2 Gc (COP-RDA) Pa · s 20240 20960Mechanical Properties

ESCR and antioxydant (AO) tests were performed on resins A and D (SeeTable 5) on homogenised fluff and on pellets. Worse product resistancewas observed with resin A due to the higher density. Some fractures arealso obtained with resin A at 100% Antarox (the average fracture timefor the samples is still of 703 hours).

TABLE 5 Resin A Resin D units Stadis AFAI Homogenised MI2 g/10′ 0.0880.0589 Fluff HLMI g/10′ 10.2 6.9 SR2 116 117 Density g/cc 0.9536 0.9508Pellets HLMI g/10′ 14.3 8.8 SR2 density g/cc ESCR F50 hr >700 >700

The ESCR was measured following the method of standard test ASTM D 1690.The tests were performed on 10 samples of each resin: 6 samples had anaverage ESCR of slightly above 700 hr and 4 samples had an average ESCRof over 1250 hr.

1. An olefin polymerization process comprising: a) providing achromium-based polymerization catalyst; b) contacting said catalyst withan alpha olefin in a polymerization reactor under polymerizationconditions with an anti-fouling polymer having an average molecularweight greater than 1,000 daltons and having i) at least one polymerblock characterized by the formula —(CH₂—CH₂—O)_(k)-wherein k is withinthe range of 1-50; and ii) at least one polymer block characterized bythe formula —(CH₂—CH(R)—O)_(n)-wherein R comprises an alkyl group havingfrom 1-6 carbon atoms and n is within the range of 1-50; wherein saidcopolymer is terminated by end groups R′ and R″, R′ is OH or a C₁-C₆alkoxy group and R″ is H or a C₁-C₆ alkyl group; and c) recovering anolefin polymer from said reaction zone.
 2. The process of claim 1wherein R is a methyl group.
 3. The process of claim 1 wherein saidanti-fouling polymer is liquid at room temperature.
 4. The process ofclaim 3 wherein said anti-fouling polymer has a molecular weight of atleast about 2,000 daltons.
 5. The process of claim 4 wherein saidanti-fouling polymer has a molecular weight of no more than 5,000daltons.
 6. The process of claim 4 wherein said anti-fouling polymer hasa molecular weight within the range of 2,000-4,500 daltons.
 7. Theprocess of claim 1 wherein the ends of said anti-fouling polymer arehydrophilic.
 8. The process of claim 1 wherein said anti-fouling polymercomprises a block copolymer characterized by formula (I) or (II):R′—(CH₂—CH₂—O)_(k)—(CH₂—CH(R)—O)_(n)—(CH₂—CH₂—O)_(m)—R″  (I)orR′—(CH₂—CH(R)—O)_(a)—(CH₂—CH₂—O)_(b)—(CH₂—CH(R)—O)_(c)—R″  (II) whereinR comprises an alkyl group; R′ and R″ are end groups as defined in claim1; k is from 1 to 50; n is from 1 to 50; m≧1; a is from 1 to 50; b isfrom 1 to 50; and c is from 0 to
 50. 9. The process of claim 8 whereinsaid anti-fouling polymer comprises a block copolymer characterized byformula (III):R′—(CH₂—CH₂—O)_(k)—(CH₂—CH(CH₃)—O)_(n)—(CH₂—CH₂—O)_(m)—R″  (III) whereinR′, R″, k, n, and m independently are as defined in claim
 8. 10. Theprocess of claim 8 wherein the anti-fouling polymer comprises a blockcopolymer characterized by the general formula (V):OH—(CH₂—CH₂—O)_(k)—(CH₂CH(CH₃)—O)_(n)—(CH₂—CH₂—O)_(m)—H  (V) where k, n,and m independently are as defined in claim
 8. 11. The process of claim1 wherein said reactor comprises a loop reactor.
 12. The process ofclaim 11 wherein said reactor comprises a double loop reactor.
 13. Theprocess of claim 1 wherein said polymerization reactor is operated at atemperature within the range from 40° to 130° C.
 14. The process ofclaim 13 wherein said reactor is operated at a pressure within the rangeof from 5 to 200 bars.
 15. The process of claim 1 wherein said polymercomprises an alpha olefin homopolymer or copolymer.
 16. The process ofclaim 15 wherein said polymer is a homopolymer of ethylene or acopolymer of ethylene and at least one C₃+alpha olefin.